The instant invention relates to automated pipe racking apparatus and more particularly to such apparatus for use to facilitate coupling and uncoupling substantially vertical lengths of pipe.
In the drilling of oil and gas wells, a string of drill pipe having a drill bit mounted on the lower end thereof is suspended from a traveling block in a drilling rig mast. The drill string is suspended from the traveling block by a swivel which enables rotational force to be applied to the drill string, typically by a rotary table at the drilling rig floor, to advance the depth of the drilled bore. As the depth of the bore increases, additional lengths of drill pipe are added to the drill string at the surface.
Periodically it is necessary to pull the drill string from the bore in order to change the drill bit or to run testing or other equipment into the bore on the end of the drill string.
When pulling drill pipe from the bore, the traveling block is raised until a stand of pipe extends above the drilling rig floor. In the usual case a stand comprises three pieces of pipe totaling approximately 90 feet in length. Next, slips are placed between the pipe and the drilling rig floor in order to suspend the drill string in the well bore from a point beneath the pipe stand which extends above the drilling rig floor. Thereafter, the connection between the pipe stand and the remainder of the drill string is unthreaded and the lower end of the stand is placed on a support pad, sometimes referred to as a setback, on the drilling rig floor. Next, a man positioned in the upper portion of the rig disconnects the upper end of the stand from the traveling block and places the upper end of the stand between a set of racking fingers which support the stand in a substantially vertical position. The traveling block is then lowered to pick up the drill string and the process is repeated until all of the pipe, in three piece stands, is supported at the lower ends thereof on the setback with the upper ends being constrained between pairs of racking fingers.
When running a new drill bit or a tool into the well bore the above-described process is reversed. That is, a man on a platform adjacent the racking fingers removes a stand of pipe and connects it to the traveling block. When the traveling block is lifted, the lower end swings into position above the well bore, the tool or bit is mounted on the lower end thereof, and the traveling block lowers the stand into the bore. Next, slips are inserted between the stand and the drilling rig floor to suspend the stand in the well bore while the traveling block is raised to permit the upper end of another stand to be connected thereto. This process is repeated until the drill string reaches the desired depth in the well bore.
The above described procedure for running a drill string into or out of a well bore poses a danger to the person working on the platform above the drilling rig floor. This job entails reaching from the platform to the center line of the well in order to connect the upper end of a pipe stand to the traveling block (and to disconnect the same therefrom) and moreover requires moving the upper end of each pipe stand between the racking fingers and the center line of the well. This is one of the most dangerous jobs on the drilling rig.
There have been a number of prior art efforts to automate one aspect or another of the procedure for running drill pipe into and out of the well bore. Some of these procedures incorporate the use of mechanical arms mounted on the drilling rig mast adjacent the racking fingers for moving the upper ends of the pipe stands between the well center line and the racking fingers. Some include lower arms or dollies for simultaneously gripping the lower end of the stand in order to move the same between the well center line and the setback. Some of the prior art devices move the stands in response to control signals generated by a computer.
All of the prior art devices suffer from several disadvantages. First, many of the prior art devices are cumbersome in their design and thus in their operation and are expensive to build. None of the prior art devices incorporates a computer controlled apparatus for moving the upper stand of pipe while permitting the lower stand to be swung in the usual fashion between the setback and the well center line. That is, prior art computer controlled devices typically include a lower gripping arm or dolly for moving the lower end of each pipe stand between the well center line and the set back. Such a design has been necessary in the past in order to coordinate movement of the upper and lower ends of the stand but such design increases the cost and complexity of the equipment.
The prior art apparatus typically includes only a single arm for manipulating pipe at the upper end of a pipe stand. Since the usual pipe storage facility includes two sets of opposed racking fingers, 180.degree. movement of the arm is required in order to access both sets of racking fingers. The speed of operation and the system design would be simplified if 180.degree. movements were not required.
The instant invention comprises apparatus for use to facilitate coupling and uncoupling substantially vertical lengths of pipe by moving the pipe between a coupled position thereof and a racking assembly. An arm assembly includes a gripping head mounted thereon for grasping a pipe. Means are provided for moving the arm assembly. The lower end of a pipe received in the racking assembly is supported by a support assembly which includes means for sensing the location of the lower end of each pipe on the support assembly. Control means connected to the sensing means and to the moving means is provided for moving the arm assembly to a preselected position dependent upon the position of the lower end of a pipe which is set on or removed from the support assembly. In one aspect of the invention, the arm assembly includes a first arm and a second arm which are extendable and retractable along axes oriented at 90.degree. to one another.